1. Field of the Invention
The present invention relates to an ink, an ink jet recording method, an ink cartridge, a recording unit, and an ink jet recording apparatus.
2. Description of the Related Art
An ink jet recording method is a method of forming images by applying ink droplets to recording media such as plain paper and glossy media. This method has rapidly come into widespread use by the reduction in cost and improvement in recording speed of ink jet recording apparatuses. Further, with the rapid spread of digital cameras in addition to the progress in obtaining high-quality images by the ink jet recording method, the ink jet recording method has been commonly used as the output method of images equal to silver halide photographs.
In recent years, further progress in obtaining high-quality images is achieved by minimization of ink droplets and improvement in the color gamut accompanying introduction of a multicolor ink. On the other hand, the demand to a coloring material and ink becomes higher, wherein severer properties are demanded in the improvement in color developabilities and reliability of clogging and ejection stability.
On the other hand, in the ink jet recording method there is a problem in that the resulting recorded matter is inferior in image storage stability. Generally, the image storage stability of the recorded matter obtained by the ink jet recording method is low as compared with silver halide photographs. In particular, when a recorded matter is exposed to light, humidity, heat, environmental gas such as ozone gas that is present in the air, etc. for a long time, there is a problem such that the coloring material on the recorded matter deteriorates and is liable to result in the change of color tone and fading of images.
In order to improve the image storage stability, particularly ozone resistance, a large number of proposals have been conventionally made. For instance, many techniques for improving the fastness of an image, particularly ozone resistance, have been suggested for a coloring material used for an ink jet ink, but these techniques do not reach such a level as to satisfy the higher level fastness required in recent years.
Further, in recent years, a demand that recorded matters are displayed on a wall or a bulletin board without being set in a frame, is increasing. In contrast, with fastness in such a level obtained by an ink widely used at present, a coloring material in an image is significantly faded by an acid gas in the air, particularly ozone, to an unacceptable level in some cases.
Fading of an image is caused primarily by a cyan ink having particularly low ozone resistance among respective inks of cyan, yellow and magenta. Therefore, many proposals for improving ozone resistance of cyan ink have been made (see Japanese Patent Application Laid-Open Nos. 2002-249677, 2002-275386, 2002-294097, 2002-302623, 2002-327132, 2003-3099, and 2003-213168). Further, a proposal has been made in which ozone resistance of an image is improved by introducing a nitrogen-containing heteroaromatic ring into a skeleton of a phthalocyanine type coloring material commonly used as a coloring material for a cyan ink (see Japanese Patent Application Laid-Open No. 2003-34758), and it is described that this phthalocyanine type coloring material may have (SO3D)m or (SO2NHR)n (wherein m=1 to 4, and n=0 to 3) as a substituent, and the above SO2NHR is a sulfonamide residual group which can form a complex with SO2NH2 or a copper ion. (In addition, the above D represents a monovalent alkali metal, ammonium, or organic ammonium). Furthermore, in order to improve ozone resistance of an image, an ink has been proposed containing a plurality of phthalocyanine type coloring materials in combination (see Japanese Patent Application Laid-Open No. 2006-328129).
Further, a technique has been proposed in which attention is concentrated on the aggregation property of a coloring material, and both ozone resistance and bronze resistance are achieved by defining a d75 value of a phthalocyanine type coloring material (see Japanese Patent Application Laid-Open No. 2006-45534). However, the level demanded by current users is increasingly raised on a day-to-day basis, and further improvement is thus required.
As described above, there is at present no proposal for such a fundamental solution as to significantly improve ozone resistance.